1) Two shortwave radio antennas broadcast identical, in-phase signals at the sam
ID: 2296297 • Letter: 1
Question
1) Two shortwave radio antennas broadcast identical, in-phase signals at the same frequency. The transmitters are 176.0 m north, and 176.0 m south of Western Ave, respectively, as shown (that is, they are separated by 352.0 m). Western Ave is 452.0 m long. Starting at the end of that avenue, a car drives north along Negundo Street, which lies parallel to the line joining the two radio antennas. The car first encounters a minimum in reception after it travels 124.0 m. What is the wavelength of the radio waves? Assume that the car and the transmitters are all at the same altitude.
http://imgur.com/gk8crtr
2) A pair of double slits is cut into a thin aluminum barrier, and coherent laser light passes through the slits. The interference pattern is observed on a faraway screen. Some ice is placed in contact with the bottom of the aluminum barrier so that it slowly cools. Thermal contraction causes the aluminum plate to become shorter in all of its linear dimensions. What happens to the interference fringes?
a the fringes stay absolutely fixed
b. outlying fringes move closer to the centerline
c. outlying fringes move farther from the centerline
d. fringes disappear
Explanation / Answer
Negundo St. is 452 m from the antenna baseline. Then since the car starts at a point of equal path-lengths to the antennas, and 124 m gets it to a point of 1/2 wavelength path-length difference. Then wavelength lambda = 2(sqrt(452^2+(176+124)^2) - sqrt(452^2+(176-124)^2)) = 175.03 m.
What this has to do with the wavelength of light is beyond me.
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